1. Low Luminosity Opportunities Andrew Brandt, U. Texas at Arlington DØ ADM November 18, 2005 “easy” “really hard”

2. Context FPD fiber trigger now working, gives possibility of unique data samples FPD will only operate routinely up until shutdown, primarily due to increased luminosity expected after shutdown (<3.5 months of operations left) Low lum period gives opportunity to maximize diffractive physics during a period of limited use to rest of experiment

3. Low Luminosity Proposal I Run with injection tune (  *=1.6m), 1 p on 4 pbar (originally 2x4 but CDF not interested), no low  squeeze, collisions by ramping down separator voltages. This particular configuration is required to minimize setup time and extra collisions. Note: If we collide P1 and A1 at DØ, P1 will collide with A2 60m later (at D1) with A3 120m later, with A4 180m later. If we collide P4 with A4, P4 will collide with A1 180m earlier (C side), etc. They (AD) have some tricks to lop off last or first bunch, may be able to scrape other bunches (they’re thinking about it). Duncan is looking at timing to understand which scenario best. Any implications at DØ, lum calc? trigger?

4. Low Lum Proposal I: “High  ” Why: Can move pots to much lower t-values (high  * means fatter beams at IP and not as fat at pots) Physics goals: Low-t elastic scattering (map out dip region), low-t single diffractive and double pomeron. Totally unique data samples. Possibility of total cross section measurement. Stats needed: Minimum one store (estimate 1-2 nb -1 for a store) uncertainties in initial lum and pot positions make predictions difficult. Proposal: Take one store at beginning of two week period, look at data and if justified take more data in second week

5. Elastic t distribution t range accessible with injection tune pot positioninteg. luminosity

6. Total Cross Section DØDØ

7. Total Cross Section Study Key issues: Low enough t for extrapolation Sufficient elastics (need 50-100k to have a chance at 2mb error) estimate 300k assuming tmin=.15 (50% trigger, 50% φ) Inelastic counting (assume 2%) Emittance (5-10  ) PU 8  50k events 0.10.2 0.5

8. Luminosity Uncertainty Brendan says: scenario 1 : --------------- -we measure cross section half way between CDF and E811 with comparable errors - exactly same experimental error as now The luminosity error would decrease from 6.5% down to about 6% scenario 2: --------------- -we measure a cross section consistent with CDF with comparable errors - a new Tevatron average is formed using only CDF and D0 -exactly same experimental errors as now The luminosity error would decrease to 5% Alternate Scenario (not Brendan): adopt DØ uncertainty since it would be the only one at current energy; error drops to 4 to 4.5%

9. Double Pomeron 2nb -1 *100ub*acc*trig eff =2000*100*.1*.5=10000 events? Could be used to distinguish different models of pomeron (phi correlations of p and pbar for example: A. Kupco, R. Peschanski, C. Royon, Phys. Lett. B606 (2005) 139

10. Low Luminosity Proposal II Run with  *=0.28 m at low lum (few E30) (This is equivalent to CDF proposal) Why: ~0 multiple interactions, low halo allows closer pot positions, intermediate t Physics goals: calibrate ξ from gaps with ξ from protons (this allows for example double pomeron with track+gap, improving acceptance) gap/cal studies in low MI environment alignment/calibration for full data sample (using large elastic sample) intermediate t-sample for physics Stats needed: 1-2 stores depending on pot positions, lum Proposal: take one store at beginning of two week period, look at data and if justified take more data in second week

11. Low Luminosity Luminosity Expect 40-100 nb -1 for a 24 hour store CDF

12. CDF Low Luminosity Proposal Context: Tokyo pots will be removed during shutdown in favor of collimators to protect silicon

13. Summary Request two types of stores to take advantage of FPD capabilities during a rare lowish luminosity running period: I) High  * for low-t elastic+diffraction II) Low luminosity for 0 MI calibration sample and intermediate t